In recent years, object-based audio systems capable of handling background sound have been proposed (see e.g., NPL 1). This technique proposes that background sound is input as a multi-channel background object (MBO) in the form of multi-channel signals, and the input signals are compressed into one channel signal or two channel signals by an MPS encoder (MPEG Surround encoder) and handled as a single object (see e.g., NPL 2).